In a modular multilevel converter (MMC) having a plurality of converters in series or parallel in a multiplexed manner to achieve a large capacity, a plurality of converter cells are connected in cascade to form arms.
In a voltage-type converter connected to an AC voltage source such as a power grid, if AC voltage outputted from the power converter is greatly different from the voltage of the AC voltage source when the voltage-type converter is interconnected with the grid, overcurrent flows in the voltage-type power converter. Therefore, for connecting an MMC that is a voltage-type power converter to an AC voltage source, not only a DC capacitor in each converter cell needs to be charged, but also the MMC needs to output voltage almost equal to the grid voltage (for example, see Patent Document 1).
Therefore, in a conventional power conversion device with an MMC configuration, it is general to initially charge a DC capacitor in each converter cell at the time of startup. In some methods for initially charging the DC capacitor, the DC capacitor is charged via a charge resistor from the AC grid (for example, see Patent Document 2 and Patent Document 3).